To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Contradictions between the booming of the wireless service requirements of users and the limited spectrum resources become increasingly sharp. Mobile operators have started to consider taking the unlicensed band as a supplement for the licensed band. Therefore, researches about deploying LTE on the unlicensed band are put on agenda. The 3GPP has begun to study how to increase the spectrum utilization ratio of the whole network via the effective carrier aggregation on the unlicensed band and the licensed band in the premise that other techniques on the unlicensed band are not affected apparently.
The unlicensed band has generally been allocated for other purposes, e.g., radar or 802.11 series Wireless Fidelity (WiFi). Thus, on the unlicensed band, the interference level is not fixed, which makes it hard to ensure the Quality of Service (QoS) of the LTE transmission. But the unlicensed band is still able to be used for transmitting data with low QoS requirement. Herein, the LTE system deployed on the unlicensed band is referred to as an LTE-U system. On the unlicensed band, it is a key problem that how to avoid interference between the LTE-U system and the other wireless system such as radar or WiFi. Clear Channel Assessment (CCA) is a collision avoidance mechanism generally adopted on the unlicensed band. One station (STA) has to detect the wireless channel before transmitting signals. The wireless channel can be occupied for transmitting signals only when it is detected that the channel is clear. The LTE-U also follows a similar mechanism, so as to ensure a low interference to other signals. In a relatively simple method, an LTE-U device (base station or user equipment) is dynamically on/off according to a CCA result, i.e., transmit signals when detecting the channel is clear, and not transmit signals when detecting the channel is occupied.
In the LTE system, especially for the downlink, in order to support link adaptation of the base station, the UE needs to report downlink Channel State Information (CSI) to the base station.
The UE measures the channel based on downlink reference signals, such as Cell specific Reference Signal (CRS) or Non-Zero Power Channel State Information Reference Signal (NZP-CSI-RS) or Zero Power CSI-RS (ZP-CSI-RS), and reports Channel Quality Indicator (CQI) to the base station.
The UE may report the CQI periodically or may report the CQI non-periodically under the trigger of the base station. The existing downlink reference signals used for channel measurement are transmitted periodically. Therefore, the UE may obtain one or more channel measurement samples according to these signals, and combine the channel measurement samples to generate a corresponding CQI and report the CQI to the base station.
It should be noted that, the above description of the background is merely used for giving a clear and complete description to the technical solution of the present disclosure and for facilitating the understanding of those with ordinary skill in the art. The description should not be regarded as well-known for those with ordinary skill in the art merely because they are placed in the background.